Sera used for this study.

The Gram-positive pathogens of the ESKAPE group, Enterococcus faecium, and Staphylococcus aureus, are well-known to pose a serious risk to human health because of their high virulence and numerous drug resistances. To narrow down the list of previously identified promising protein vaccine candidates, a combination of several antigen discovery approaches was performed, in particular a “false positive analysis” of peptides generated by trypsin shaving with a subtractive proteome analysis. The final list of nine potential antigens included AdcAau, a protein performing the same function as AdcAfm, an already discovered antigen in enterococci. Bioinformatic analyses revealed that AdcAau and AdcAfm share a sequence identity of 41.2% and that the conserved regions present a high antigenicity. AdcAau was selected for further investigation and the results reported in this manuscript demonstrate the opsonic properties of AdcAau-specific antibodies against the Staphylococcus aureus strain MW2, as well as their cross-binding and cross-opsonic activity against several S. aureus, E. faecium, and E. faecalis strains. The experimental design revealed several promising vaccine candidates, including the newly identified S. aureus antigen, AdcAau. The study shows its potential as a vaccine candidate to prevent infections by dangerous Gram-positive ESKAPE pathogens.